Mechanical decoupling device for attachment to electroacoustic transducers

ABSTRACT

A device for attachment of electroacoustic transducers in casings immersed under water and effecting mechanical decoupling through flexible or deformable portions such as rubber or elastomer rings between the vibrating parts and their support.

te States Patent 1 1 Tocquet et a1. 1 1 Oct. 30, 1973 [54] MECHANICALDECOUPLING DEVICE FOR 3,539,980 11/1970 Massa, Jr. 340/10 X C M N oELECTROACOUSTIC 2,917,642 12/1959 Wright et aL... 310/91 X 3,328,6106/1967 Jacke et al 310/9.1 X TRANSDUCERS 3,337,844 8/1967 BaltakisSID/9.1 x [76} inventors: Bernard Tocquet, Sanary; Marcel 3,031,5914/1962 y e! Personnic Toulon both of France Straube X 3,546,497 12/1970Craster 310/9.1 X [22] Filed: Nov. 8, 1971 3,321,189 5/1967 Scarpa310/91 X [21] Appl. No.: 196,344

Primary Examiner-J. D. Miller Assistant Examiner-Mark O. Budd [30]Foreign Application Pnority Data Attorney-Eric H. Waters et a1.

Nov. 6, 1970 France 7039959 [52] 11.8. CI. 310/89, 310/9.l, 340/10 [57]ABSTRACT [51] Int. Cl. H04r 17/00 [58] Field of Search 310/8 2 8 3 8 7 Adevice for attachment of electroacoustlc transduc- 0/9 ers in casingsimmersed under water and effecting me- I chanical decoupling throughflexible or deformable [56] References Cited portions such as rubber orelastomer rings between UNITED STATES PATENTS the vibrating parts andtheir support. 3,474,403 10/1969 Massa et a1. 340/10 6 Claims, 7 DrawingFigures N fl J i //////1H/// //l W 11 f i I T T\ H, i m Z/c w? i; do '0,,2 3

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DF0/?M/4770A/ paw/02E 7/45 UFmm) MECHANICAL DECOUPLING DEVICE FORATTACHMENT T ELECTROACOUSTIC TRANSDUCERS BACKGROUND OF THE INVENTION 1.Field of the Invention The invention relates to electroacoustictransducers and specifically to the support of a vibration generatorthereof in a support casing.

2. Description of the Prior Art Conventional electroacoustic transducersare provided with a stack of piezoelectric ceramic plates forming agenerator, and the generator is mounted in a casing adapted for use inunderwater acoustic operations. The generator is mounted in the casingor onto the frame of an antenna by means of an attachment which mustserve to decouple the generator subjected to sustained vibrations andits support casing. Two constructions of such attachment are currentlyin use; the first being a wholly flexible attachment by means of an O-ring member and the second being a rigid attachment to the casing at thevibration node by means of an electrode intercalated between thepiezoelectric ceramic plates.

These constructions do not satisfactorily meet the necessaryrequirements. A wholly flexible attachment is possible only fortransducers subject to low ambient pressures and therefore not immersedto great depths in a body of water. Moreover, such attachment does notprovide protection against impact, implosions or explosions, and toattain such protection it becomes necessary to use additional deviceswhich greatly lower the efficiency.

A rigid attachment at the nodal point is used to a large extent and thispartly resolves these latter problems but it down not providesatisfactory decoupling. In fact, it is not always possible to mount thesupport electrode precisely at the nodal point, if only because theelectrode is of a certain thickness. Moreover, the position of the nodalplane itself is not permanent and it varies in relation to thefrequency. This makes the attachment of the transducers for a very largepass band a delicate operation.

The difficulties presented by both these arrangements usually result ina deterioration of the electroacoustic efficiency which is all the morepronounced the wider the transducer band and the greater the depth ofimmersion.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a system for attaching an electroacoustic transducer either inits sealed casing or directly to an antenna frame to remedy the abovedeficiencies and additionally to increase electroacoustic efficiency.

The invention comtemplates as an attachment means a mechanical parttermed an electrode support, comprising two rigid portions, one integralwith the stack of piezoelectric plates, and constituting one of theelectrodes, and the other integral with the casing or more generallywith the transducer support. Between these two portions is a connectionhaving a high mechanical impedance allowing slight relative movements ofthe portions of the order of -100 millimeters under the force ofhydrostatic pressure at maximum depths of the order of 50 to 100kilonewtons for a diameter of several centimeters. Further, when theassembly has to withstand impact, explosions or implosions, stop meansare arranged for limiting displacement of the portion integral with thepiezoelectric stack.

In the course of construction, the connecting element of high mechanicalimpedance is mounted close to the nodal plane, under various workingconditions, thus assuring optimal acoustic decoupling of thepiezoelectric stack relative to the support.

The aforesaid mechanical attachment is constructed in terms of theconditions of manufacture, use and environment in order to attainsuitable impedance and mechanical properties.

Such mechanical attachment can be made of one or more metal or hardplastic rings in which two or more deep grooves are machined in planesperpendicular to the axis of the rings, leaving between them only a thinpartition of material having the desired flexibility to provide therequired relative movement between the two rigid portions located onboth sides of the grooves. The elastic connection between the two rigidportions can also be obtained by one or more discs of the same materialor of different materials respectively secured, as by cementing orwelding, at their inner and outer peripheries to the respective portionsto be connected.

The attachment can also be constituted of two or more stiff or rigidrings nesting into each other with a predetermined clearance andassembled by means of a rubber or elastomer ring fixedly attached, bycementing or preferably by hot vulcanization under pressure, to theopposite faces of the two attachment rings.

One of the attachment rings is made integral with the piezoelectricstack with which it forms one of the electrodes, by precast cementingwith the whole of the transducer.

The other attachment ring is rigidly attached to the sealed casing whichserves as a housing for the transducer, or to the antenna frame. Theconnection between the two rings is obtained by the rubber or elastomerring.

The mechanical clearance between thesetwo attachment parts when they arenested into each other is calculated so as to meet the followingrequirements: the friction between the two parts must be zero ornegligible; the clearance between the parts must not allow the rubber orelastomer to seep out by creepage under the action of the forces due tothe surrounding hydrostatic pressure exerted on the electrode throughthe outside vibrating surface of the transducer.

The size, shape and characteristics of the rubber or elastomer ringjoining the two parts are selected so as to obtain the required highmechanical impedance.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectionthrough a transducer equipped with an electrode support according to theinvention,

FIG. 2 is a sectional view of the support by itself,

FIG. 2a is an enlarged sectional view of a modified ring used in thesupport,

FIG. 2b shows another modified ring,

FIG. 3 is a graphical representation of deformation of the support withrespect to applied force,

FIG. 4 is a sectional view of another embodiment of an electrodesupport, and

FIG. 5 is a graphical representation similar to FIG. 3, for the supportof FIG. 4.

DETAILED DESCRIPTION Referring to FIG. 1, herein is illustrated anembodiment of a transducer with an electrode support I! adapted for useas a small size electroacoustic transducer in underwater operations atwhich the maximum hydrostatic force on the electrode is 32,000 newtons.

The transducer comprises a conventional stack of piezoelectric ceramicplates P assembled as a unit on shaft 8 and sewing as one of theelectrodes. A counterweight W is assembled with the unit and theassembly is mounted in a metal casing C by the electrode support I-!constructed in accordance with the invention. The casing C is containedwithin an airtight enclosure E carrying an acoustic element F as isconventional.

The electrode support I-I comprises an inner member 1 made of analuminum alloy and fixedly secured to the stack by an adhesive or thelike. The support I-I further comprises an outer member 2 made of steel.The outer member 2 is threaded externally and is screwed into the casingC of the transducer. A very compact unit is thus obtained. The inner andouter members I and 2 are joined together by a ring 3 which is fixedlysecured at its opposite faces respectively to members l and 2. The ring3 is secured to the members 1 and 2 by adhesives, or preferably by hotvulcanization under pressure. The ring 3 is made of an elastomersubstance such as Neoprene having a Shore hardness of 50 on scale A,after the vulcanization at high temperature and intense pressure. Theinner and outer members are interfitted with minimal clearance of lessthan 0.5 mm and offer little or no frictional resistance to theirrelative longitudinal displacement.

FIG. 3 graphically illustrates the relative movement of the inner andouter members 1 and 2 as a function of the applied force. Up to forcesof 50,000 newtons, such relative movement is very low and linear inrelation to the applied force, even after a considerable number ofcycles.

Th electroacoustic performance of the transducer using this attachmentarrangement of the electrode holder shows the efficiency to be improvedby more than percent as compared to identical transducers equipped withthe standard attachment.

FlG. 2a shows a modification of the ring of the support and in FIG. 2athe ring 3a is formed with inner and outer grooves 31 and 32respectively in a plane perpendicular to the axis of the ring 30 todefine a thin wall of material 33 providing the requisite flexibility.The ring 311 can be made of metal or hard plastic material.

FIG. 2b shows another modification of the ring and herein the ring 3b iscomposed of a plurality of juxtaposed discs 41, with clearancestherebetween, of the same or different materials and respectivelysecured, e.g., by cementing or welding, at their inner and outerperipheries to the inner and outer members I and 2.

A second embodiment of the electrode support is illustrated in FIG. 4and is adapted for a decoupling electrode of a transducer on whichforces up to 90,000 newtons may be applied. This embodiment provides forimpact resistance limiting the displacement of the inner member of theelectrode support under the effect of separation forces.

In the embodiment of FIG. 4, the inner member 1' is made of aluminumalloy as is also the outer member 2'. The ring 3' is made of Neopreneand has a Shore hardness of 60 on Scale A after vulcanization undernormal conditions of temperature and pressure. The transducer isattached to the casing by two screws engaged in threaded bores 5 inmember 2'. A circlip 6 is engaged within the outer member 2' forlimiting relative displacement between members I and 2' in onedirection. The members I and 2' are formed with opposed respectiveshoulders 7a and 7b which limit relative movement of members 1' and 2'in the opposite direction. Thus, protection is provided againstexcessive relative displacement or implosion forces.

FIG. 5 shows graphically the relative displacement of members 1 and 2'with respect to applied force. The displacement is low and perfectlylinear with respect to force up to 100,000 newtons.

What is claimed is:

1. In an electroacoustic transducer adapted for immersion in a body ofwater to a considerable depth and having firstly a vibration assemblyformed by a stack of piezoelectric elements alternating with electrodesand having a nodal plane and means for transmitting vibration to thesurrounding water and secondly a leak proof casing, said vibrationassembly and said casing being bodies of revolution around the same,center line; the provision of means for supporting said stack withinsaid casing, said means comprising an inside ring fastened to said stackclose to said nodal plane; an external ring fastened to said casing,said external and internal rings being of substantially equal thicknessand facing each other, each comprising two portions of differentdiameters interjoined along a face perpendicular to said center line andnesting within one another parallel to said center line with very closeclearance between the external face of the inside ring and the internalface of the external ring, said faces of each of the two ringsperpendicular to the said center line and facing one another beingspaced from one another at a particular distance so that the externalsurface of the inside ring and the internal surface of the external ringdefine a housing therebetween; and an elastic coupling means located insaid housing, said elastic coupling means having a high mechanicalimpedance and being able to resist the stresses due to high hydrostaticpressure.

2. A support means as claimed in claim 16 wherein said elastic couplingmeans comprises an elastic plate located in said housing, said platehaving opposite faces which are perpendicular to said center-line, saidfaces being adhesively secured to said faces of the two rings which areperpendicular to the said center line and facing one another.

3. A support means as claimed in claim 1 wherein said elastic couplingmeans comprises plates of elastic material of equal dimensions, stackedin said housing and fastened circumferentially internally and externallyrespectively to the external periphery of the said inside ring and tothe internal periphery of the said external ring defining the housing.

4. A support means as claimed in claim l comprising stop means forrestricting the relative movement of the inside ring and of the externalring to prevent implosion of said elastic coupling means.

5. A support means as claimed in claim Al wherein said stop meanscomprises firstly, a clip engaged in a slot provided in said casing tolimit the movements of the inside ring parallel to the center line inone direction and secondly a shoulder located on the external ring andfacing a shoulder on the inside ring to limit the movements of saidrings parallel to the axis in opposite directions.

6. A support means as claimed in claim 5 wherein said inside andexternal rings each have a second surmeasured along the axis of thetransducer is less than the distance measured in the same directionseparating the faces which define the housing in which said ealstic faceperpendicular to the center of each, the second 5 cmpling means ismounted-

1. In an electroacoustic transducer adapted for immersion in a body ofwater to a considerable depth and having firstly a vibration assemblyformed by a stack of piezoelectric elements alternating with electrodesand having a nodal plane and means for Transmitting vibration to thesurrounding water and secondly a leak proof casing, said vibrationassembly and said casing being bodies of revolution around the same,center line; the provision of means for supporting said stack withinsaid casing, said means comprising an inside ring fastened to said stackclose to said nodal plane; an external ring fastened to said casing,said external and internal rings being of substantially equal thicknessand facing each other, each comprising two portions of differentdiameters interjoined along a face perpendicular to said center line andnesting within one another parallel to said center line with very closeclearance between the external face of the inside ring and the internalface of the external ring, said faces of each of the two ringsperpendicular to the said center line and facing one another beingspaced from one another at a particular distance so that the externalsurface of the inside ring and the internal surface of the external ringdefine a housing therebetween; and an elastic coupling means located insaid housing, said elastic coupling means having a high mechanicalimpedance and being able to resist the stresses due to high hydrostaticpressure.
 2. A support means as claimed in claim 16 wherein said elasticcoupling means comprises an elastic plate located in said housing, saidplate having opposite faces which are perpendicular to said center-line,said faces being adhesively secured to said faces of the two rings whichare perpendicular to the said center line and facing one another.
 3. Asupport means as claimed in claim 1 wherein said elastic coupling meanscomprises plates of elastic material of equal dimensions, stacked insaid housing and fastened circumferentially internally and externallyrespectively to the external periphery of the said inside ring and tothe internal periphery of the said external ring defining the housing.4. A support means as claimed in claim 1 comprising stop means forrestricting the relative movement of the inside ring and of the externalring to prevent implosion of said elastic coupling means.
 5. A supportmeans as claimed in claim 4 wherein said stop means comprises firstly, aclip engaged in a slot provided in said casing to limit the movements ofthe inside ring parallel to the center line in one direction andsecondly a shoulder located on the external ring and facing a shoulderon the inside ring to limit the movements of said rings parallel to theaxis in opposite directions.
 6. A support means as claimed in claim 5wherein said inside and external rings each have a second surfaceperpendicular to the center of each, the second faces being oppositeeach other at a spacing which as measured along the axis of thetransducer is less than the distance measured in the same directionseparating the faces which define the housing in which said ealsticcoupling means is mounted.